Enhanced Stratosphere/Troposphere Coupling During Extreme Warm Stratospheric Events with Strong Polar-Night Jet Oscillation

• Published in: Atmosphere
• Main Authors: Dieter H.W. Peters, Andrea Schneidereit, Alexey Y. Karpechko
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2018
• Subjects: warm stratospheric events; major sudden stratospheric warmings; polar-night jet oscillation; northern annular mode; Arctic oscillation; EP-flux divergence; ERA-Interim; CMIP5; MPI-ESM-LR; Meteorology. Climatology; QC851-999; Arctic; polar night
• Online Access: https://doi.org/10.3390/atmos9120467; https://doaj.org/article/3c46947e4dbd44418ab18d5f78d5d1e3

Extreme warm stratospheric events during polar winters from ERA-Interim reanalysis and CMIP5-ESM-LR runs were separated by duration and strength of the polar-night jet oscillation (PJO) using a high statistical confidence level of three standard deviations (strong-PJO events). With a composite analysis, we demonstrate that strong-PJO events show a significantly stronger downward propagating signal in both, northern annular mode (NAM) and zonal mean zonal wind anomaly in the stratosphere in comparison with non-PJO events. The lower stratospheric EP-flux-divergence difference in ERA-Interim was stronger in comparison to long-term CMIP5-ESM-LR runs (by a factor of four). This suggests that stratosphere⁻troposphere coupling is stronger in ERA-Interim than in CMIP5-ESM-LR. During the 60 days following the central date (CD), the Arctic oscillation signal was more intense during strong-PJO events than during non-PJO events in ERA-Interim data in comparison to CMIP5-ESM-LR runs. During the 15-day phase after CD, strong PJO events had a significant increase in stratospheric ozone, upper tropospheric zonally asymmetric impact, and a regional surface impact in ERA-Interim. Finally, we conclude that the applied high statistical threshold gives a clearer separation of extreme warm stratospheric events into strong-PJO events and non-PJO events including their different downward propagating NAM signal and tropospheric impacts.